yeah if link throws his boomerang right as he drops from the ledge, it catches him and he grabs the ledge right back. however it keeps you invincible from when you leave the ledge (sorta like when mk drop down uairs) and the boomerang's hitbox is still there, still doing an attack, but your invincible.

and yes ic cg are banned, you can grab and do a smash attack but thats it